Feed mechanism



Dec. 26, 1950 R. E. PRICE FEED macwmxsm Filed Feb. 18, 1949 (Ittorneg pump circuit throughout and thuselimina-te leakage in the circuit.

Patented Dec. 26, 1950 FEED MECHANISM .Ralph Price, I-Iighfield. Md, assignor to Landis Tool Company, Wayneshoro, Pa.

Application February 18, 1949, Serial No. 77,218

(Cl. (iii-52) 6 Claims. 1

"This invention relates .to feed mechanisms for .machine tools, particularly grinding machines.

It relates more particularly to the operation of .ssuch mechanisms for that portion of a feed move- -ment which occurs during the actual grinding operation.

These feed movements are often as slow as .00005" per second. The accuracy of the grinding operation is-therefore dependent on a uniform "and accurately controlled feed movement. In

orderto accomplish this,it is necessary to have amniform delivery of oil to the feed mechanism.

In previous feed mechanisms, two factors have "interfered-with satisfactory operation of the feed -mechan'ism: (l) variation in fluid delivery due to variation of viscosity caused by changes in temperatureof the fluid and (2) variation in fluid "deli-very due 'to variation of pressure in the system. 'Wherea. slow feed is required such as that described above-the volume of fluid involved is very small. Leakage through even close clear- :ances between running-parts of a pump account for a large percentage of this volume.

It is, therefore, an object of this invention to "It is a. further object to provide a delivery of oil to the feed mechanism which will beless affected by temperature or pressure in the system. It isa further object to provide a differential subject to uniform pressure A'further object is to provide a constant flow .of "fluid in said circuit regardless of variation in --viscosity-of the fluid or fluctuations of pressure required to operate the feed.

'The term-differential pumps as used herein means-pumps differing slightly in output and com nected in series so that the smaller pump pumps from-thelarger to'the extentof its capacity. The

remaining'fluid, which is'the difference in output of the two pumps, is directed to the feed mechanism.

Figure 1 ShOIWS the invention asapplied to control'o'fthe flowof fluid to one end of said cyl- *I'tank or reservoir is supplied bypump lilto which is connected a relief valve i. Fluid under pressure from said pump-zpasses through line 5 to reversing valve 16 which in ,the position shown .directs said fluid through line H to the rodend .of cylinder If! to causepiston is .to move to the left. iExhaust fluid is discharged from thehead end of cylinder 18 through line 26, check valve.-

2!, reversing valve 16 and exhaust line 22. To move piston 59 in the opposite direction, valve 15 is shifted to the left to connect line I! with exhaust. Fluid from line 15 cannot pass through line 219 because of check valve '2 l. Fluid for moving piston is to the right is supplied by pump [8 at a pressure determined-by the setting of relief valve H and at a rate determined vby the capacities'of differential pumps PI and P2.

The-output of *Pi is slightly greater than that of P2. FillidilfOmPi passes through line 30 to the inlet side of P2. F uid from P2 passes through line 3! to the inlet side Of1P l- A balancing valve consisting of valve piston 35 havingequal areas at opposite endsthereof is slidahly mounted in cylinder 36. One end of said cy'inder is connected through-line 3'? to line 31. The other end of said cylinder is connected through line 38 to line '30. Adjacent the end of cylinder 35 to which line-38 is connected is a discharge passage 39 leading to line 26 and the head end of cylinder l8. "Fluid under pressure is supplied to this meter-ing pump circuit from line l5 through line 455 to line 3!.

"In operation, P2 pumps from Pl to the extent of its capacity. The excess fluid passes through line sate shift valve i-idto uncover passage 39 and per- -mit the flow of fluid to the head endof cylinder Since the input of ,Pi and the output of P2 are connected together andto constant pressure and since the output of PI and the intake ofPZ are connected together and to theend of the balancing valve by line 38 which reflects the pressure of the opposite end of valve 35 which is connected by line :3? to constant pressure line 3|. the input and output of both pumps P! and P2 are all subject to equal pressure. The only difference in pressure anywhere in the circuit is that required to cause flow of the oil. Leakage from pressure drop with the variables encountered due to varying pressures and viscosities is'therefore minimized. With these variables reduced to a minimum, the fluid supplied to the feed mechanism is substantially the exact difference in output of the two pumps. The result of this arrangement is to provide a'substantially uniform feed at extremely slow speed.

In Figure 2 the same elements are utilized, but the circuit is somewhat different. Fluid under pressure is supplied by pump l0 through line 15 to reversing valve it from which it is directed through line 56 to the headend of cylinder IS to cause piston is to move to the right. Exhaust fluid irom the rod end of cylinder 58 passes through line 5! to the metering pump circuit.

The rate of flow of said exhaust fluid into the metering pump circuit is the same as the dis- When valve 55 is shifted to the left, it directs fluid under pressure from line 55 through line 53, check valve 3 and line 5! to the rod end of cylinder is to reset the feed mechanism by shifting piston 'i '3 to the left. At the same time fluid under pressure from the same source enters the metering pump circuit through line 3! to replace the fluid discharged from balancing valve 3'5.

Thus, the metering pump circuit may be applied as a unit to any feed mechanism either to control the supply of fluid during the feed movement or to control the exhaust during said feed movement. In one case, the discharge from the balancing valve is the fluid supplied for driving the piston. In the other case, the rate of discharge from the balancing valve to a sump determines the rate of exhaust from cylinder is during the feed movement. In both cases, the metering pump circuit is maintained under a constant pressure through a connectio with pump it. Since the circuit is closed and maintained under constant pressure, leakage ceases to be a critical factor in its functioning. The balancing valve 35 permits a discharge of a flXed volume of fluid under all conditions, and thus variation in viscosity has no eifect on the delivery of fluid for actuating the feed mechanism.

I claim:

1. A feed mechanism for a machine tool comprising a piston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate of said re ative movement during a feeding operation including differential metering pumps connected in a circuit in which fluid lines connect the outlet of each pump with the inlet of the other, a connection between said circuit and said supply of fluid under pressure, a balancing valve including a piston and cylinder having equal areas at each end a connection from one end of said valve to one of said lines, a connecticn from the other end of said valve to the other line, and connections between said balancing valve and one end of said feed cylinder for conducting a vo ume of fluid equal to the difference in output of said pumps.

2. A feed mechanism for a machine tool comprising a pston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate of said relative movement during a feeding operation including differential metering pumps connected in circuit in which fluid lines connect the outlet of each pump with the inlet of the other, a connection from said circuit to said fluid supply and to said feed cylinder, a ba ancing valve connected in parallel with said pumps, and connections between said pumps and one end of said feed cylinder including said balancing valve for controlling the flow of exhaust fluid from said cylinder,

3. A feed mechanism for a machine tool comprising a piston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate or said relative movement during a feeding operation including diflerential metering pumps connected in a circuit in which fluid lines connect the outlet of each pump with the end of the other, a connection from said circuit to said fluid supply and to said feed cylinder, a balancing valve connected in parallel with said pumps, and connections between said pumps and one end of said feed cylinder including said balancing valve for directing fluid under pressure to said cylinder.

4. A feed mechanism for a machine tool comprising a piston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate of said relative movement during a feeding operation including diiferential metering pumps in a circuit in which fluid lines connect the outlet of each pump with the inlet of the other, a connection from said circuit to said fluid supply, a balancing valve connected in parallel with said pumps for maintaining a substantially uniform pressure in said circuit and for discharging a volume of fluid equal to the differential output of said pumps and connections between said pump circuit and said feed cylinder.

5. A feed mechanism for a machine tool comprising a piston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder, including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate of said relative movement during a feeding operation including diiferential metering pumps connected in a circuit in which fluid lines connect the outlet of each pump with the inlet of the other, a connection from said circuit to said fluid supply and to said feed cylinder, a baancing valve in said circuit for maintaining substantially equal pressures in all parts of said circuit.

6. A feed mechanism for a machine tool comprising a piston and cylinder, one of which is attached to the part to be moved, a supply of fluid under pressure for causing relative movement between said piston and cylinder, including a reversing valve for directing said fluid alternately to opposite ends of said cylinder, means for controlling the rate of said relative movement during a feeding operation including differential metering pumps connected in a circuit in which fluid lines connect the outlet of each pump with the inlet of the other, a connection between said circuit and said supply of fluid under pressure, a balancing valve connected in said circuit in parallel with said pump for maintaining equal pressures in said fluid lines, whereby the fluid from said fluid supply is metered exactly in accordance with the capacities of said differential pumps.

RALPH E. PRICE.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Blood May 26, 1936 

